About 43 million individuals in the US currently suffer from disabilities due to arthritis. Cartilage defects are the major source of pain in the affected joints. Current treatments, whilst alleviating some of the clinical symptoms, prove insufficient to cure the underlying irreversible cartilage loss. Stem cells represent a unique source for restoration of cartilage defects. However, a major challenge with various approaches of stem cell and chondrocyte transplants is death of the transplanted cells with clearance by the immune system. The overall goal of this project is to develop a non-invasive and clinically applicable MR imaging technique, which provides an early diagnosis of complications of the engraftment process of matrix associated stem cell implants (MASI). The hypothesis is that viable and apoptotic MASI in arthritic joints demonstrate distinct signal characteristics on MR images, when combined with cell-specific MR contrast agents. In our current funding period, we have established labeling techniques for stem cell transplants with iron oxide nanoparticles and gadolinium chelates, and we have defined distinct signal characteristics of labeled viable and apoptotic MASI. During the new funding period, we will continue to use this approach to identify and develop strong candidate contrast agents for clinical translation. We plan to apply for an IND for clinical translation of the most promising approach by the end of this new funding period. In our pursuit of clinically applicable imaging approaches, we will first evaluate stem cell loss and/or apoptosis early after MASI via direct labeling of transplanted stem cells with the FDA-approved iron oxide nanoparticle ferumoxytol (Feraheme). In a second step, we will evaluate a novel caspase-sensitive MR contrast agent regarding its sensitivity to detect stem cell apoptosis in MASI with an arthrographic imaging approach. In a third step, we will identify failed MASI indirectly, via MR detection of the migration of iron oxide labeled bone marrow macrophages into MASI. Complementary optical imaging studies as well as confocal microscopy, immunohistochemistry and spectrometry studies will be performed to elucidate biological and physicochemical changes of the investigated cell transplants that lead to the observed MR signal characteristics. Results should be immediately helpful in the preclinical assessment of new stem cell based therapies for arthritis treatment, in the design of related clinical trials for hMSC therapy of arthritis, and ultimately, in the assessment of those hMSC therapy regimens in clinical practice. By exploiting novel, clinically applicable cell tracking techniques as a new too to monitor stem cell engraftment outcomes non-invasively in vivo, we anticipate significantly improving and accelerating the development of successful therapies for cartilage regeneration in patients, and ultimately, alleviating long term disabilities and related costs to our society. Sinc we address a generalized novel concept for imaging stem cell engraftment, results might not only impact patients with MASI but also patients with a variety of other (stem) cell transplants.